World's oldest plant fossil discovered in India

A team of researchers has discovered fossils of 1.6 billion-year-old probable red algae in India, indicating that advanced multicellular life evolved on earth much earlier than previously thought.

The study, appeared in the open access journal PLOS Biology, found two kinds of fossils resembling red algae - first type is thread-like, the other one consists of fleshy colonies - in uniquely well-preserved sedimentary rocks at Chitrakoot in Central India.

The scientists were able to see distinct inner cell structures and so-called cell fountains, the bundles of packed and splaying filaments that form the body of the fleshy forms and are characteristics of red algae.

"You cannot be 100 percent sure about material this ancient, as there is no DNA remaining, but the characters agree quite well with the morphology and structure of red algae," said Stefan Bengtson.

The earliest traces of life on Earth are at least 3.5 billion years old. These single-celled organisms, unlike eukaryotes, lack nuclei and other organelles.

Discoveries of early multicellular eukaryotes have been sporadic and difficult to interpret, challenging scientists trying to reconstruct and date the tree of life.

The oldest known red algae before the present discovery are 1.2 billion-year-old.

The Indian fossils, 400 million years older and by far the oldest plant-like fossils ever found, suggest that the early branches of the tree of life need to be recalibrated.

"The 'time of visible life' seems to have begun much earlier than we thought," Stefan Bengtson stated.

The presumed red algae lie embedded in fossil mats of cyanobacteria, called stromatolites, in 1.6 billion-year-old Indian phosphorite.

The research group was able to look inside the algae with the help of synchrotron-based X-ray tomographic microscopy.

Among other things, they have seen regularly recurring platelets in each cell, which they believe are parts of chloroplasts, the organelles within plant cells where photosynthesis takes place.

They have also seen distinct and regular structures at the centre of each cell wall, typical of red algae.